1. Field of the Invention
The present invention relates to a metal substrate for an oxide superconducting wire, an oxide superconducting wire, and a method of manufacturing the oxide superconducting wire.
2. Description of the Related Art
As for the method of manufacturing a superconducting wire by making use of an oxide superconductor, there is known a method wherein an intermediate layer having a controlled crystal orientation is formed on an elongated metal tape, and an oxide superconducting layer is formed on the intermediate layer. As a typical example of the superconducting tape-like wire obtained by this method, there is known a tape-like wire which can be obtained through a process wherein a stabilized zirconia (YSZ) is deposited on a Hastelloy tape by means of an ion beam-asisted deposition (IBAD) method, thereby controlling the crystal orientation of zirconia with c-axis thereof being oriented with the tape and a- and b-axes thereof being aligned with the tape (in-plane orientation), and a Y123(YBa2Cu3O7−y)-based oxide superconducting film is formed on the zirconia layer by means of a laser abrasion. Since this tape-like wire is excellent in crystal alignment of a- and b-axes thereof, the critical current density (Jc) would become as high as 0.5-1.0×106A/cm2 under the conditions of 77K and zero Tesla.
This method, however, is accompanied with a drawback that the film-forming rate is as very slow as 0.001-0.01 m/h, thereby raising various problems in industrial viewpoint if it is desired to manufacture a long wire (see for example, Y. Iijima et al., Appl. Phys. Lett. Vol. 60(1992), 769).
There is also reported one example wherein an oxide layer is formed on the surface of nickel tape or copper tape by oxidizing the surface thereof, and an oxide superconducting layer is formed on this oxide layer functioning as an intermediate layer (see for example, A. Ginsbach et al., Physica. CI85-189(1991), 2111).
The gist of this method resides in that an oxide film is formed on the surface of metal tape only through the oxidation of the surface of the metal tape and that the oxide film is utilized as an intermediate layer in the same manner as the aforementioned YSZ or CeO2. This method is suited for mass production and hence considered as a practical method.
However, according to this method, the enhancement of orientation of oxide crystal is not taken into consideration at all. As a result, the Jc of oxide superconducting layer formed on this oxide film by means of sputtering method is at most 1×103A/cm2 or so, which is as low as about one thousandth of that of the aforementioned high orientation tape wire.
With a view to overcome these problems, there has been proposed a method of manufacturing a superconducting wire wherein a polycrystalline metal substrate is subjected to rolling work, heated at a temperature of 900° C. or more in a non-oxidizing atmosphere to obtain a rolled aggregate structure where the {100} plane is parallel to the rolled surface and the <001> axis is parallel to the rolling direction (hereinafter referred to as {100}<001> crystal orientation), and further heated at a temperature of 1000° C. or more in an oxidizing atmosphere to obtain an oxide crystal layer consisting of an oxide of polycrystalline metal where 90% or more of the {100} plane is oriented so as to become parallel to the surface of the aforementioned polycrystalline metal substrate at an angle of 10° or less, and an oxide superconductor layer is deposited on this oxide crystal layer (see for example, JP Laid-open Patent Publication (Kokai) No. 11-3620 (1999)).
However, even with this method, the orientation of the oxide crystal is insufficient, thus failing to obtain a satisfactory critical current density.
The present invention has been accomplished under these circumstances and hence, the objects of the present invention are to provide a metal substrate for an oxide superconducting wire which makes it possible to form an oxide superconducting wire of high critical current density, an oxide superconducting wire exhibiting a high critical current density, and a method of manufacturing the oxide superconducting wire.